What Is Serotyping And How Does It Relate To Genotypes, Strains, Salmonella, And E.Coli? 

Do you want to learn more about what serotypes are?

More often than not, the classification of different microscopic organisms is typically based upon a variety of different factors of the cells – including the structure of the cells, their ecology, as well as what their mode of reproduction is.

With this being said, by taking these factors into account, it is possible to group certain cells found within an organism into a specific classification to differentiate them from other cells within the same organism.

What Is Serotyping And How Does It Relate To Genotypes, Strains, Salmonella, And E.Coli? 

It is important to make sure that these classifications are made so that any similar micro-organisms (such as immune cells or virus cells) that can often be very similar in appearance, can often have different antigens which means it is important to group each type of organism into a sub-species within a certain organism. 

In this article, we are going to be taking a closer look at what a serotype is, what it is used for, as well as comparing it to various other organisms to help you gain a better understanding of why it is so important. Let’s begin.

What Is A Serotype?

Before we jump any further into this article, we first think that it would be a good idea to clearly outline what a serotype is.

As we have already briefly outlined above, a serotype is a term that is used to describe a variety of sub-species of cells found within one species.

More specifically, a serotype is usually used to refer to a group of organisms within one species that has the exact same kind and amount of surface antigens. 

So, with all of that being said, serotypes are various strains that are often described as being single isolates (or simply subspecies) within one pure culture that contains specific antigens that other cells within the same species do not.

By doing this and creating various serotypes within one species, it means that the various types of cells can be easily identified and distinguished from one another. 

Still, even though serotypes are used to group various organisms together within one species, it is very important to note that serotypes are different from strains.

This is because a strain of cells is a group of organisms that are single isolates from pure cultures, and contain the same, identical phenotypic and genotypic traits and characteristics.  

Plus, as we have already touched upon in a previous paragraph above, cells such as virus cells, immune cells, and bacteria cells can often appear to be near identical upon first impressions, so taking the time to figure out which cells contain the same surface antigens can prove to be very helpful when distinguishing between the different cells that are present within one species or organism. 

The Importance Of Antigens And Serotypes

Following on from the point above, antigens are very important when serotyping (otherwise referred to as epidemiological typing) simply due to the fact that there are almost always changes that take place between different types of surface antigen – even if they happen to be situated on the same organism. 

These different types of antigens are able to release a variety of different antibodies, and this means that they can also be identified via identification of the certain antibodies that the antigens release when they are triggered.

With all of this being said, it is important to make sure that you have a good understanding of antigens when trying to understand serotypes, as it can help you to better understand why serotyping is so useful. 

Let’s take a closer look at what an antigen is below:

What Are Antigens?

What Are Antigens?

Now that we have briefly outlined what the importance of antigens are, we are now going to be outlining what an antigen is.

To cut a long story short, an antigen is basically a type of substance that has the capability to initiate an immune system reaction by triggering specific antibodies or T cells to form in one area of the body/organism. 

Generally speaking, the majority of antigens are typically made out of mainly protein, although there are some antigens that can also be made up of something that is known as polysaccharides.

In addition to this, it is highly common for antigens to be found on certain parts of microorganisms that contain viruses or bacteria, so it is very common to discover antigens on the walls of cells, on the flagella of cells or even on the surface of them. 

Following on, it is also important to note that despite the fact that antigens typically tend to be very small in nature, they are very complex and made up of several different layers that serve different functions and purposes. 

For example, one layer of antigens contains something that is known as the antigenic determinant, which is the specific part of an antigen that is able to be recognized by B cells, T cells, and antibodies.

Without it, antibodies would be unable to do their job effectively, as they would not be able to respond to any triggers due to being unable to recognize the antigens releasing them.

In addition to this, it is also worth noting that the antigenic specificity of the molecules also resides in the antigenic determinant part of the antigen, as this is the only part of the antigen that is able to be effectively recognized by the paratope of the immune molecules and antibodies that respond to the triggers.

To follow, antigen epitopes are typically split into two different groups. To help you understand the differences between the two a bit better, let’s take a look at both groups of antigen epitopes below:

  • Continuous Epitopes: The first group of antigen epitopes includes the continuous epitope, which are very small peptide fragments that have the capability to bind to various antibodies. This means that they are typically made of a variety of amino acids.
  • Discontinuous Epitopes: The second group of antigen epitopes is discontinuous epitopes, which typically tend to contain residues that are not continuous in sequence, which therefore means that they often appear to be bent and folded in their appearance and formation. Still, while this might be the case, they offer the same purpose as the continuous epitopes which we have already described above.

Before we move on to the next section, a few points to keep in mind:

  1. Not all antigens can trigger an immune response: It is important to remember that not all antigens have the ability to trigger an immune response.
  1. Not all molecules can be immunogenic: There are some molecules that are antigenic but do not contain the relevant properties in order to be immunogenic.

Moving on, even though there are some molecules that do not have the ability to produce an immune response, there are some factors that do allow an antigen to have immunogenic properties. Let’s take a look at them below:

  • Degradability: In order for a molecule to have an immunogenic ability, they need to be able to degrade.
  • Complex design: While this isn’t something that all immunogenic molecules have, the majority of molecules that can produce an immune response tend to have a complex composition of many parts and different layers.
  • Foreign substance: In order for a molecule to be immunogenic, it will need to be of a foreign nature.
  • Molecule size of between 14,000 and 600,000 Da: Molecules that fall within this size range have been shown to have the most active immunogens.

Now that you have a better understanding of molecules and antigens, as well as how they relate to serotyping, let’s move on to strains and genotypes.

Strains Vs Serotyping

Even though a species tends to refer to a type of organism that contains all of the same biochemical, genetic and phenotypic traits, a strain differs slightly as it isolates a certain sub-species that is based on a variety of traits that include enzymes, functions, and, of course – serotyping. 

When compared directly to serotypes, serotypes are different from strains and genotypes because they are created from directly characterizing the antigen properties, while identifying a strain is far more complex and takes into account a variety of different factors in order to make the determination. 

To follow on from this point, even though it is important to note that the genotype and phenotypic characteristics are extremely important in determining a strain, unlike serotypes, strains are able to maintain their identity even if there are changes to some of their phenotype and genotype compositions.

In addition to all of the above, when taking into consideration that strains (which can also be referred to as isolates) have the ability to adjust their genetic makeup by taking on new genetic material from their surroundings, it is often far more difficult and complex to identify a strain of microorganisms than it is to identify a serotype.

Before we move on any further, here are some points to take away:

  • Even though the identification of serotypes and strains are often different (with strains often being far more complex and taking into account several different factors, while serotypes are usually merely identified by their surface-level antigens) it is worth keeping in mind that strains can often be categorized and identified by determining what their respective serotype is.
  • Given the fact that strains are often determined by a very complex process that takes into account a variety of different characteristics and traits in order to identify and group a strain, it means that the physiological properties are very important when determining strains.

Now that we have explored the differences between strains and serotypes, let’s move on to taking a closer look at the differences between serotypes and genotypes.

Genotypes Vs Serotyping

Genotypes Vs Serotyping

If you’re not already familiar with what a genotype is, or you would simply like to have a refresh on your knowledge of what they are – then we are going to be covering what they are (as well as how they differ and relate from serotypes) in this section.

To cut a long story short, a genotype is essentially a term that is used to describe the full set of genes that comprise one organism.

More often than not, this specific set of genetic data is often the main influence of what the characteristics of the organism overall are going to be, especially with regards to its surrounding environment. 

To follow on from this point, this genetic data is typically passed down from one parent organism to the child organism, and this is a cycle that goes on and on for every new organism made.

However, even though this is the case, do keep in mind that the more strains (or organisms) that are made, the higher the likelihood will be of the passed down genetic information being changed or alerted.

This can happen to any strain, although it is most typically observed within new strains of bacteria.

Moreso, in the event that the genetic information gets passed down and altered in some way, this means that it may impact and alter some of the overall characteristics of the organism as a whole.

Still, along with the chances of genetic information being changed as it gets passed down from organism to organism (or strain to strain) it is also important to keep in mind that it is also possible for a variety of external factors within the surrounding environment to also play a role in altering the original genetic material. 

To provide you with an example of what we mean by this, let’s say there are two strains that contain practically identical genotypes.

Due to the slightly altered genetic information that was changed either from being passed down from the parent organism or by external factors within the environment, the two strains might have entirely different characteristics despite sharing nearly the same or identical set of genes.

With all of this being said, it is therefore important to note that the genotype may have the ability to influence both the strain and the serotype of any given organism, only so long as the genetic material of the said organism is one of the direct influencers of a certain trait/characteristic.

Now that we have covered genotypes, let’s move on to microorganism serotypes, as well as their respective strains and genotypes – including Salmonella and E.Coli.

Microorganism Serotypes, Including Genotype And Strain

Now that we have taken the time to cover what serotypes are, as well as how they are directly related to genotypes, phenotypes and strains – we are now going to be taking a closer look at Salmonella and E.Coli. Let’s start with Salmonella:


If you weren’t already aware, Salmonella is a type of bacteria that typically occurs mainly in the gut. It is often caused by a specific serotype that then results in the person experiencing food poisoning and other symptoms. 

To help you understand this a little better, the genes that comprise a Salmonella cell typically include gram-negative, facultative anaerobes that are generally considered to have been created by a surrounding E.Coli bacteria within the surrounding environment.

With that being said, as we have already mentioned above, the Salmonella cells are some of the most prevalent in causing food poisoning all over the world.

To follow on from all of this, it can also be said that, despite the fact that this species of cells can easily survive on their own as commensals, they can also be pathogens that can exist and be passed between both humans and animals.

From a medical standpoint, salmonella is identified as the following:

  • Family: Enterobacteriaceae
  • Order: Enteorbacteriacaea
  • Phylum: Proteobacteria
  • Domain: Bacteria

In addition to all of the above, it is also worth noting that Salmonella is typically made up of two species that are the following main species: Salmonella enterica, as well as Salmonella bongori.

However, just like with other bacteria and viruses, they can typically be grouped into sub-species due to external and internal genetic information changes – and this leads to the need for sub-species to be grouped into the following categories:

  • Genotypes
  • Strains
  • Serotypes

In addition to this, there are currently over 2500 serotypes that have been identified from Salmonella, with all of them having the potential to cause food poisoning in humans.

All of these species have three main antigens that include flagellar antigen, somatic antigen, and Vi antigen.



E.Coli was first discovered in 1885 and is a gram-negative bacillus that is usually found in the lower intestines of humans, as well as animals.

E-Coli is a normal part of the culture within the lower intestine, although there are a variety of strains that can cause illness. These strains typically contain genetic information that has been modified from either internal or external factors. 

Here is a medical classification of E.Coli:

  • Domain: Bacteria
  • Family: Enterobacteriaceae
  • Order: Enterobacteriaceae
  • Class: Gammaproteobacteria
  • Phylum: Proteobacteria

At the time of writing this article, there are currently over 50,000 serotypes of E.Coli that are currently known to be in existence.

However, the number that are pathogenic and have the ability to cause disease in humans and animals is far lower. The antigens seen in E.Coli are H-antigen and the K-antigen.

The Bottom Line

We’ve made it to the end! To sum up, everything that we have covered above, even though serotypes, genotypes, and strains do not necessarily mean the same thing (as they each are terms that are used to describe different things) it is important to still note that they are similar in the sense that they are directly related to the overall organism that they are held within.

To follow, Genotypes are directly connected to the genetic information of the organism that is being identified, which is the full set of genes that are able to directly influence the traits and characteristics of the organism’s strain and serotype.

Therefore, it can be said that the genotype of an organism has the ability to directly affect the type of strain, as well as the characteristics of the serotypes that might fall with it. 

Along with this, it can also be said that serotypes can be used as an additional categorization of the strains found within an organism.

This simply comes down to the fact that strains tend to contain different microorganisms that can also have different antigens, so there will be a need to further categorize due to these changing molecules and genetic information.

Thank you for taking the time to read through this article, we hope that it has been helpful to you in better understanding serotypes.

Jennifer Dawkins

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